Electron tube device provided with a periodic permanent magnet focussing means and magnetic flux temperature compensating means



Sept. 15, WT@ RYUzo ORUI 3,52%,97

ELECTRON TUBE DEVICE PROVIDED WITH A PERIODIC PERMANENT MAGNET FOCUSSING MEANS AND MAGNETIC FLUX TEMPERATURE COMPENSATING MEANS Flled June 26, 1968 United States Patent C U.S. Cl. 313-8 4 Claims ABSTRACT F THE DISCLOSURE A periodic permanent magnet focussing assembly for use in traveling-wave tubes. The assembly is comprised of substantially cylindrical-shaped permanent magnets arranged in tandem fashion so that their central axes are colinear and so that the polarity of adjacent magnets are the same. A plurality of annular-shaped pole pieces are interspersed between adjacent magnets and have central axes which are colinear with one another as well as being colinear with the axis of the permanent magnet members. A hollow substantially continuous elongated cylinder 0f magnetic material is positioned within the hollow Space defined by the permanent magnet members and pole pieces such that its longitudinal axis is substantially colinear with the longitudinal axes of the pole pieces and permanent magnets. The magnetic metallic cylinder is formed of a material having a negative temperature coefficient of permeability so that the magnetic field developed by the permanent magnet members within the interior space of the magnetic cylinder is maintained substantially constant in spite of changes in ambient temperature which normally affects the magnetic field generated by the permanent magnet members. The magnetic cylinder assures positive symmetrical alignment of all components of the` focussing means as well as simplifying the assembly of the focussing structure.

The present invention relates to electron tube devices and more particularly to a novel permanent magnet focussing structure for use with electron tube devices of the type employing a long electron beam odic magnetic field.

The present invention is primarily concerned with electron tube devices and especially those devices of the type commonly referred to as traveling-wave tubes which are employed as amplifying devices. Such amplifying devices normally are comprised of a traveling-wave tube containing a long electron beam within the tube interior and having a periodic permanent magnet focussing means arranged exterior to the tube. In such traveling-wave tube amplifiers, an electromagnetic wave which is propagated in the interior of the tube enters into hollow cylindrical cavities which are defined by magnets employed in the focussing means and by p'ole pieces within the focussing means which are interspersed between adjacent magnets. The entry of the electromagnetic wave into the cavities has an adverse effect upon the frequency characteristics 0f the traveling-wave tube amplifiers.

In order to prevent such adverse effects it has been conventional practice to electrically shield the cavities from the traveling-Wave tube through the use of a cylinder formed of a non-magnetic metal which surrounds and is in close proximity to the tube envelope. In traveling-wave tube amplifiers of the above categories, it has been found that the magnetic flux supplied by the individual magnet members of the focussing assembly to the traveling-wave focussed by a peritube varies with changes in temperature. This is especially so in the case where magnets of the barium-ferrite type are employed. These variations result in a significant deterioration of the electron beam focussing function.

The present invention is characterized by providing an electron tube device employing a periodic permanent magnet focussing means in which the unfavorable infinence on the frequency characteristic of the device is minimized by providing means within the focussing assembly which maintains electron beam focussing regular irrespective of temperature changes which may be encountered during operation.

The present invention is basically comprised of an electron tube device having a vacuum space containing a long electron beam, means for coupling said electron beam with an electric wave, and a periodic permanent magnet focussing means disposed so as to surround the vacuum space. The focussing means includes a cylinder which is made of a magnetic metal having a negative temperature coefficient of magnetic permeability characteristic. The cylinder is positioned between the vacuum space and the focussing device so as to extend substantially in the axial direction of the focussing means and over its entire length.

The above mentioned magnetic metallic cylinder prevents the electric wave in the electron tube from entering into the cavities existing within the focussing means and additionally, maintains the constancy of the focussing means magnetic field irrespective of temperature changes.

It is therefore one object of the present invention t0 provide a novel improved focussing means for use in electron tubes of the traveling-wave type wherein the electric field coacting with the long electron beam is prevented from entering into cavities existing within the focussing means and wherein the magnetic field developed by the focussing means is maintained constant in spite of temperature changes which occur during operation.

Another object of the present invention is to provide a novel permanent magnet focussing means for use in electron tubes especially of the traveling-wave tube type wherein a magnetic metallic cylinder provided within the assembly is disposed to surround the vacuum space containing the long electron beam so as to prevent the electric field coacting with the long electron beam to enter into cavities existing within the focussing means structure and which is further characterized by having a negative temperature coefficient of magnetic permeability to maintain the magnetic field generated by the focussing means constant irrespective of changes in temperature encountered during operation.

These as well as other objects of the present invention will become apparent when reading the accompanying description and drawings in which:

FIG. 1 is an axial sectional view of one emodiment of the present invention.

FIG. 2 is an axial sectional view of another embodiment of the present invention showing only the structure of the focussing means for purposes of simplicity.

FIG. l shows one preferred embodiment of the present invention 'which is commonly referred to as a travelingwave tube device 10 and which includes a periodic permanent magnet focussing assembly 14 having axially magnetized hollow cylindrical permanent magnets 11 and annular pole pieces 13 which are provided with axial protrusions 12. 'Ihe permanent magnets are arranged so that poles of like polarity are disposed in face to face relationship for all neighboring permanent magnets. Magnetic polarities have been indicated in FIG. 1 by the letters N and S to clearly identify the orientation of the permanent magnets, each to the other. The pole pieces 13 are positioned between each pair of neighboring permanent magnets so that their axial protrusions are partially telescoped within the hollow interior of the adjacent pair of permanent magnets. l

A traveling-wave tube velope which Ibounds and defines a vacuum space 16 provided to permit an electron beam to pass therethrough. A metallic cylinder 19` formed of a magnetic metal such as iron-nickel alloy which has a negative temperature coeicient of magnetic permeability, is placed between the periodic permanent magnet focussing means 14 and the traveling-wave tube envelope 17. The outer diameter of metallic cylinder 19 is selected so as to snugly t the center hole of each annular pole piece 13. The axial length of cylinder 19 is substantially equal to the entire axial length of the periodic permanent magnet focussing means 14. It should beunderstood that the length ofthe traveling-wave tube structure may be greater than that shown in FIG. l in which portions thereof have been broken away for purposes of simplicity. The metallic cylinder 19 need not necessarily be a one-piece cylinder as shown in the drawing, but maybe comprised of a plurality of cylinders abutting one another in an end to end fashion.

' The function of the present invention is as follows:

The total magnetic flux produced by each hollow cylindrical-shaped permanent magnet 11 is divided into a first magnetic ux 21 which is arranged to lie on or near the longitudinal axis of the structure which passes through the vacuum space 16 of the traveling-wave tube. A second magnetic flux path 22 passes through the metallic cylinder 19; a third magnetic flux path 23 passes between the axial protrusions 12 of pole pieces 13 on both sides of the magnet 11; and a magnetic flux path 24 extends between the poles of the magnet around the outer periphery.

Considering the condition of a rise in ambient temperature of the traveling-wave tube device, the total magnetic flux 20 produced by permanent magnet 11 is reduced, while the permeability of the metal cylinder 19 is decreased as a result of its negative temperature coeflicient characteristic. As a result, the magnetic ux branch 22 passing through metallic cylinder 19 is reduced The reduction in the magnetic uxes appearing in branches 21 and 22 is equalized rby selecting the magnetic characteristic of the material employed to form the metal cylinder 19 and/or by adjusting the thickness of the metal cylinder 19 in direct relationship to thetemperature characteristic of the permanent magnet members 11. Although the magnetic flux 21 lying on or near the longitudinal axis of the structure is slightly affected 'by the influence on permeability of the metal cylinder 19 due to temperature changes because of its passing through the metal cylinder 19 substantially at right angles to the longitudinal axis, the thickness of metal cylinder 19` is chosen to be so thin in comparison with the distance between the axial projecting portions of adjacent pole pieces that the magnetic reluctance present when the magnetic flux- 21 passes through the metal cylinder 19 in the radial direction is very much smaller than that present when the magnetic llux 22 passes through the metal cylinder 19 in the axial direction. Thus, the temperature change affecting the magnetic reluctance which has a bearing on the magnetic flux 21 canbe neglected as a practical matter.

The metal cylinder 19 provided in the embodiment of FIG. l Ifurther serves as a shield which prevents the electric wave propagating within the traveling-wave tube 18 is-comprised of a sealed en-A 18 from entering into the annular-shaped cavities 26 dened by the interior surface of permanent magnet 11, the opposing vertical sides of pole pieces 13 and the exterior surface of metal cylinder 19. This shielding effect greatly improves the frequency :characteristics of the traveling-wave tube device.

Another important advantage of the present invention resides in the fact that the alignment of the pole pieces and hence the mutual coaxial positioning of the elements comprising the periodic permanent magnet focussing means 14 is. greatly simplified due to the fact that metallic cylinder 19 which snugly receives the pole pieces 13 automatically provides colinear alignment between the central axis of each pole piece and the longitudinal axis of the cylinder 19y and hence of the tube 17. The telescoping cooperation between pole pieces 13 and magnets 11 further cooperates to automatically align the permanent magnet members so that their central axes as well, are colinear with the longitudinal axis of cylinder 19 and hence of tube 17. The metal cylinder 19 additionally has the signicant effect of correcting the axial asymmetry of the magnetic flux 21 disposed on or near the longitudinal axis of the structure which would otherwise have an adverse ellect upon the electron beam 15 passing through tube 17 and which arises from the asymmetry in the magnetic property of permanent magnets 11 and/or the inequality of contact or misalignment between the magnets 11 and pole pieces y13.

FIG. 2 shows an alternative embodiment of the present invention in which the shape of the annular pole pieces 13 is altered from that shown in FIG. 1. Basically, the annular pole pieces 13` have their axial protrusions removed and have central openings to thereby yield a ilat ring-shaped conguration. The central openings of the ilat annular pole pieces 25 and the permanent magnets 11 are of substantially the same diameter. Otherwise the arrangement of permanent magnet members and pole pieces are substantially identical to that shown and described with respect to FIG. 1. The metal cylinder 19 in the embodiment of FIG. 2 is formed of a magnetic metal having a negative temperature coeicient of magnetic permeability. The cylinder is provided with an outer diameter selected in relationship to the inner diameters of pole pieces 2'5 and permanent magnets 11 so that each of these elements 1.1 and 25 rather snugly lit around the cylinder 19.

While the embodiment of FIG. 2 has been found to provide all the advantages of the embodiment of `FIG. 1, the merits of the embodiment of FIG. 2 reside in the fact that the ease of manufacturing pole pieces 25 is greatly simplified. The assembly of the arrangement of FIG. 2 is likewise greatly simplified and the overall device is of smaller diameter resulting in miniaturization of the structure 'while at the same timestill providing good frequency characterstics of the electron tube device.

Both of the embodiments may further be modified so as to employ the metallic cylinder 19 as the envelope for l delining the vacuum space 16 of the electron tube thereby very much intensified focussing magnetic iield on the longitudinal axis thereof as well as providing a miniaturized electron tube device due to the fact that it is possible to reduce the inner diameters of both the hollow cylindrical permanent magnets and the annular pole pieces since the cylinder 19 may bev reduced to have the same diameter as the envelope 17 which it replaces (and eliminates).

Although there has been described a preferred embodiment of this novel invention, many variations and moditications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

What is claimed is:

1. An electron tube device having elongated means surrounding and defining a vacuum space provided for the passage of a long electron beam therethrough;

a periodic permanent magnet focussing means surrounding the means defining said vacuum space for generating a periodic magnetic field along the path of said electron beam;

a hollow metallic cylinder formed of a magnetic material having a negative temperature coefficient of magnetic permeability being positioned between the means defining said vacuum space and said focussing means for compensating for changes in the field strength in the region of the electron beam caused by any temperature changes encountered during operation of the electron tube device.

2. The device of claim 1 wherein said periodic permanent magnet focussing means is comprised of a plurality of hollow cylindrical-shaped permanent magnets and annular-shaped pole pieces, each of said pole pieces having axial protrusions extending in opposing directions from the opposing surfaces of said pole pieces around its center opening;

said permanent magnets and pole pieces being arranged in alternating fashion so as to substantially form an elongated cylindrically-shaped assembly with the axial protrusions of said pole pieces being received by the central openings of the permanent magnet members;

the outer surface of said metallic cylinder being adapted to engage the inner periphery of said pole pieces so as to accurately position and support said permanent magnet members by means of the axial protrusions provided around the interior periphery of said pole pieces;

the length of said metallic cylinder being substantially equal to the length of the pole piece-permanent magnet assembly constituted of the plurality of pole pieces and permanent magnets.

3. The device of claim 1 wherein said periodic perma- 45 annular-shaped flat pole pieces whose thicknesses are much less than the axial length of each permanent magnet; the central opening of each pole piece having an inner diameter substantially equal to the hollow opening of said permanent magnets;

said permanent magnets and pole pieces being arranged in alternating fashion so as to form a composite of substantially cylindrical-shaped assembly;

the outer surface of said metallic cylinder being adapted to engage the interior periphery of each pole piece and the interior surface of each hollow permanent magnet so as to support said composite assembly and accurately position each component thereof relative to one another.

4. An electron tube device having elongated envelope means surrounding and defining an evacuated space provided for the passage of a long electron beam therethrough;

a periodic permanent magnet focussing means surrounding the envelope means defining said vacuum space for :generating a periodic magnetic field along the path of said electron beam;

at least that portion of said envelope means contiguous with said periodic permanent magnet focussing means being comprised of a hollow cylinder formed of a mganetic metal having a negative temperature coefiicient of magnetic permeability designed to compensate for changes in the field strength in the region of the electron beam caused by any temperature changes encountered during operation of the electron tube device.

References Cited UNITED STATES PATENTS 2,843,775 7/1958 Yasuda 313-84 2,964,670 12/1960 Bliss 313-84 X.

3,215,906 11/1965 Taber 313-84 X FOREIGN PATENTS 1,427,456 12/ 1965 France.

JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner Us. c1. XR. S15- 3.5, 335-217 

